The invention relates to a motor vehicle power train including a drive source such as a combustion engine with a driving shaft, a driven unit with a driven shaft such as a transmission with a transmission input shaft, as well as at least one electromechanical energy converter interacting with the power train, and at least one clutch that is arranged in the torque flow path between the driving shaft and the driven shaft and serves to couple and uncouple the torque flow between the drive source and the driven unit.
Arrangements of this kind are known from the German laid-open application DE-OS 32 30 121 as hybrid drives with an electric motor and a combustion engine, or from the German patent DE-PS 41 12 215 as combustion engines with a starter-generator.
Depending on the specific layout, the electro-mechanical energy converter may be arranged either coaxially surrounding the rotational axis of the combustion engine—as known for example from the German laid-open application DE-OS 33 35 923—, or aligned along a separate axis of rotation parallel to the rotational axis of the combustion engine, as known from the French laid-open application FR-OS 81 19324.
When using the electromechanical energy converter to start the combustion engine, in order to make better use of the limited amount of available torque, the interactive connection to the power train, e.g., a belt-, friction-, or gear drive, is usually run at a transfer ratio where the electro-mechanical energy converter turns faster than the drive source, the latter being for example a combustion engine. As soon as the combustion engine is running and the electro-mechanical energy converter is operated in the generator mode, it is advantageous to operate the electro-mechanical energy converter at a transfer ratio that is optimized for the generator mode in order to increase the degree of efficiency, which requires the use of a ratio-changing rotary transfer mechanism.
A proposed arrangement according to the German patent DE-PS 41 12 215 includes a planetary gear mechanism in which the change of transfer ratios is controlled from the outside by way of a clutch that is actuated by an additionally required actuator motor. The additional transducer- and control means required with this solution lead to an increase in weight as well as cost.